Mouse Sperm May Hold the Key to a Male Birth Control Pill

A future where men might bear equal responsibility for pregnancy prevention just got a little closer. In a new study from Osaka University, scientists report that when they gave male mice a drug to inhibit a sperm-specific protein—one found in both mice and humans—the mice became infertile. When the mice stopped taking the drug, their fertility returned in just one week.

Scientists have figured for a while that the protein, calcineurin, was a crucial player in the male fertility game. But calcineurin exists in many forms in the testes, making it difficult to isolate the types that only affect sperm. Researcher Haruhiko Miyata and his colleagues identified the sperm-specific type of calcineurin and found that without it, the mouse’s sperm became ineffective without affecting the mouse’s capacity to get it up.

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The drug’s effect on mouse sperm underscores just how weirdly lifelike sperm can be. Without proper calcineurin, a sperm cell can’t swim properly, and its midsection can’t bend enough to get through a mouse egg’s membrane. Even in vitro fertilization is impossible with these mutated sperm. In Miyata’s study, mice became infertile within four to five days of their first drug dose, which indicates that the protein affects developing sperm cells, not mature ones.

Seventeen percent of U.S. women take oral contraceptives, which have long been the most common birth control method in the country, barely edging out sterilization. Vasectomies remain a popular and nearly 100 percent effective form of male birth control, but a pill would be far less invasive and perfect for temporary or intermittent use. Giving people who produce sperm the opportunity to take charge of their own birth control—and giving women a break or a backup—would mark a huge step forward for gender equity in pregnancy prevention. And a pill that works by inhibiting a sperm-specific protein would be a lot less of a pain than today’s oral contraceptives, which mess with hormones that can affect the entire body.